1. Field of the Invention
The present invention relates generally to the production of fertilizers, and more particularly to the preparation of chelated micronutrients, such as zinc, iron, manganese, magnesium, copper, calcium, and the like, for use in fertilizers.
Fertilizers usually consist of one or more of three primary nutrients: nitrogen, phosphorus, and potassium. In certain applications, it may be dsirable to add sulfur as a fourth primary nutrient. In addition to the primary nutrients, secondary nutrients (usually referred to as "micronutrients") are often added to the fertilizer in order to supplement elemental deficiencies which may exist in particular soils. As the need for micronutrients varies greatly from locality to locality, it is frequently desirable to provide micronutrients as discrete supplements which may be added to a primary fertilizer composition immediately prior to application in the field. Such supplemental micronutrients should be stable, compatible with a wide variety of primary fertilizers, and easily taken up by the plants to which they are applied.
Heretofore, such micronutrients, which typically are metal ions, have been provided as chelates with conventional chelants. While generally effective, such chelants do suffer from a number of problems. In particular, metal chelants of the prior art often display a relatively low uptake by the plants to which they have been applied, usually in the range from about 20 to 30%. In calcerous soils, the chelants become associated with magnesium and calcium ions, while in acidic soils, the chelants become associated with aluminum. In both cases, such association inhibits utilization of the micronutrient. In addition to the poor utilization, conventional metal chelants frequently provide an irregular crop response, are sometimes phytotoxic, and can precipitate when combined with certain incompatible fertilizer compositions. In addition, such metal chelants are generally unsuitable for foliar application.
For these reasons, it would be desirable to provide improved micronutrient chelants which provide for a high efficiency of uptake, are non-phytotoxic, are stable even when mixed with a wide variety of primary fertilizers, and which may be applied foliarly to plants with success.
2. Description of the Background Art
European patent application EPO No. 0164908, published on Dec. 18, 1985, describes the preparation of certain extracts of leonardite ore which are useful as compositions for promoting and modifying plant growth. These compositions are useful as a starting material in preparing the metal chelants of the present invention. Schnitzer (1980) Colloques Intertionaux du C.N.R.S., pgs. 229-234, describes the behavior of both fulvic and humic acids in soil.